Period length and amplitude characteristics of cycles of vocal fold vibration during phonation are being analyzed to determine how these are altered in patients with different types of vocal fold pathology. Types of vocal fold pathology being examined include: laryngeal nodules and polyps, lower motor neuron neuropathologies involving the nucleus ambiguous, upper motor neuron disease increasing vocal fold rigidity, unilateral recurrent laryngeal nerve paralysis, essential tremor affecting the larynx, spastic dysphonia, and vocal fold edema. The purpose is to determine how alterations in the morphology of the vocal folds and neurologic control affect the vibrations during phonation, in an effort to improve understanding of the physilogy of normal and pathological phonation. Hardware and software acoustic signal processing systems have been developed to allow for extraction of frequency and amplitude perturbation as well as computations of indices of tremor in phonation. Nasopharyngolaryngoscopic videotape recordings during connected speech provide interpretation of the types of phonatory pathology in various neurologic disorders. Studies are evaluating 1) which acoustic measures of phonation could be used in the identification of phonatory pathology, 2) which measures reflect perceptual ratings of voice disorders in different types of laryngeal pathology, 3) which measures are sensitive to changes in vocal fold morphology, and 4) how changes in vocal fold mass and tension alter the patterns in vocal fold vibration.